Solid-state compact servosystem

ABSTRACT

A servosystem having solid-state components includes means for summing an alternating command signal with a motor shaft position signal and when the resulting difference signal exceeds a predetermined threshold drivers are actuated for applying to the motor a voltage having a polarity in accordance with the phase of the difference signal relative to a reference. The voltage is cut off when the motor is at null, whereupon inertia drives the motor past null to provide a difference signal of opposite polarity so that the motor is driven in the opposite direction until it again passes through null, reversing the voltage thereto with the result being that full voltage is applied to the motor until the null is reached.

Unite States mm [72] Inven or A x D ll h k 3,406,309 10/1968 Martens 318/18 X (20.835) Livingston, NJ. 3,260,912 7/1966 Gregory 318/599 [21]Appl. No. 862,208 3,363,158 l/1968 Potma 318/616 [22] Filed Sept. 30,1969 3,391,317 7/1968 Bell 318/619 [45] Patented Aug. 17, 1971 PrimaryExaminer-Ben amin Dobeck [73] Asslgnee The Bendix CnrporafionAttorneys-Anthony F. Cuoco and Flame, Arens, Ham,

Smith and Thompson [54] SOLID-STATE COMPACT SERVOSYSTEM 2 Claims, 1Drawing Fig.

ABSTRACT: A servosystem having solid-state components in- [52] 11.5. CI.318/608, eludes means for Summing an alternating command Signal 318/614,3318/65 with a motor shaft position signal and when the resulting dif-[51] Int. Cl. Gosh 5/01 ference Signal exceeds a predetermined thresholddrivers are of Search 1 t t d f t th motor a lt g h i g a p l ity 20-41ZOAZO' 20-370 in accordance with the phase of the difference signalrelative [56] Reerences Cited to a reference. The voltage is cut offwhen the motor is at null,

whereupon inertia drives the motor past null to provide a dif- UNITEDSTATES PATENTS ference signal of opposite polarity so that the motor isdriven 3,940,028 6/ 1960 Parzen 3.18/28 X (20.440) in the oppositedirection until it again passes through null, 3,237,070 2/1966 lnaba etal. .318/ 18 X (20.415) reversing the voltage thereto with the resultbeing that full 3,239,735 3/1966 Raider et a1. 3.18/18 X (20.415)voltage is applied to the motor until the null is reached.

. g2 POWgR l I5 SUPPLY DRIVER 2 IOA 10 i I? as 34 c 9 l JPHASE SWITCH TDV 7 DET. I |0B l DRIVER-Y l3 7 I I 12 T 16 I 7 4 DEVICE DELAY NETWORKPATENIED mm 7 l9?! v 3, 600, 659

POWER H '5 SUPPLY DRIVER 3 IO 36 34 j PHASE swncn M on BRAKE DRIVER I 13T7 ,6 g 4 6 I POSITION SENSING DEVICE DELAY NETWORK IN VENTOR.

ALEX DANCHUK A rroM/E SOLID-STATE COMPACT SERVOSYSTEM BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates toservosystems and, more particularly, to servosystems having solid statecomponents, and having reduced size and weight and minimal power losses.

2. Description of the Prior Art Servosystems now known in the art useservoamplifiers which, for high power applications, are large in sizeand incur considerable power losses. Modern requirements call forsmaller and lighter systems and systems which operate with increasedaccuracy.

SUMMARY OF THE INVENTION This invention contemplates a servosystem ofsolid-state construction and having means for summing an AC commandsignal with a servomotor shaft position signal for providing adifference signal. The phase of the difference signal relative to areference signal is detected, and when the difference signal exceeds apredetermined threshold clockwise or counterclockwise drivers, dependingon said detected phase, are actuated. The drivers operate a switch forapplying a voltage of appropriate polarity to the servomotor. When theservomotor is at null the voltage is cutoff, but inertia drivers themotor past null so that a difference signal of opposite polarity isdetected. The voltage to the motor is thereupon reversed to initiallyslow the motor and to ultimately drive the motor in the oppositedirection until the motor again drives through null reversing thevoltage to the motor. In this manner full voltage is applied to themotor until null is reached to provide a servosystem having improvedaccuracy. Improved null stability is achieved by applying braking actionto the motor at null conditions.

One object of this invention is to provide a servosystem of solid stateconstruction having reduced size, minimal power losses and increasedaccuracy.

Another object of this invention is to provide a servosystem of the typedescribed having improved null stability.

Another object of this invention is to provide a servosystem havingsmall power consumption components for minimizing power losses and forsubstantially reducing the cost of the system.

The foregoing and other objects and advantages of the invention willappear more fully hereinafter from a consideration of the detaileddescription which follows, taken together with the accompanying drawingswherein one embodiment of the invention is illustrated by way ofexample. It is to be expressly understood, however, that the drawingsare for illustration purposes only and are not to be construed asdefining the limits of the invention.

DESCRIPTION OF THE DRAWINGS The single figure in the drawing is a blockdiagram of a servosystem according to the invention.

An AC command signal E, which may correspond, for purposes of example,to an aircraft flight condition signal is applied to a summing means 2.Signal E has a phase in accordance with the direction of the command. Aposition sensing device 4 is connected by suitable mechanical means 6 toa torquer motor 8 and is connected by a conductor 7 to summing means 2.Position sensor 4 may be a linear potentiometer for sensing the angularposition of the motor shaft and for providing at conductor 7 acorresponding electrical signal. Summing means 2, which may be a simpleresistance, transformer or operational amplifier in differentialamplifier configuration sums signal E and the signal from positionsensing device 4 and provides at an output conductor 9 an AC signalcorresponding to the difference therebetween. Solid state differentialamplifiers suitable for purposes of the inven tion are described atpages 111-120, Transistor Manual published in 1964 by the GeneralElectric Company.

Summing means 2 is connected through conductor 9 to an input terminal10A of a phase detector 10. Phase detector 10 has another input terminal108 connected to a suitable AC reference source 12. When the signal fromsumming means 2 exceeds a predetermined threshold, phase detector 10provides an output at either an output conductor 11 or at an outputconductor 13, depending on the phase of the signal from summing means 2.Phase detector 10 is of the type which includes an operational amplifierused as a threshold device for comparing the signal from summing means'2to a fixed level reference voltage and further includes a pair ofoperational amplifiers for phase detection whereby AC signalproportional to the phase difference between the signal from summingmeans 2 and the reference voltage from source 12 is provided at one ofthe conductors 11 or 13, depending on the phase of the signal fromsumming means 2. A solid-state device suitable for the purposes of phasedetector 10 is shown in FIG. 7-26, Pulse, Digital and SwitchingWaveforms, Milman and Taub, McGraw-l-lill 1965, modified as will beunderstood by those skilled in the art and as indicated at page 260.

Conductorsll and 13 are connected to corresponding drivers 14 and 16,and which drivers include high input impedance amplifiers which may bedescribed at page 102, FIG. 4.7, 4.8, Transistor Manual, supra, forprotecting the signal channel from loading effects. Drivers 14 and 16further include demodulators or converters for providing DC voltages atrespective output conductors 15 and 17. A device employingsemiconductors and suitable for the purposes of drivers 14 and 16 isdescribed in U.S. Pat. No. 3,525,921 issued Aug. 25, 1970 to H. B.Wattson and assigned to The Bendix Corporation, assignee of the presentinvention. It will be understood that driver 14 will provide a voltageat output conductor 15 if phase detector 10 provides an output atconductor 11 and driver 16 will provide a voltage at conductor 17 ifphase detector 10 provides an output at conductor 13. The effect ofdrivers 14 and 16 is to drive motor 8 in either clockwise orcounterclockwise directions as will hereinafter become evident.

Conductors 15 and 17 are connected to a switch 23, and which switch 23is connected to a power supply 22 providing suitable positive andnegative DC motor driving voltages. Switch 23 may be an electricalmechanical relay or transistorized switch such as. described at Chapter6, Transistor Manual, supra, responsive to the voltages at conductors 15or 17 to apply voltage of proper polarity from power supply 22 to motor8 to drive the motor. It will be understood that when voltage of onepolarity is applied to motor 8, the motor is driven clockwise and whenvoltage of the opposite polarity is applied, the motor is drivencounterclockwise.

Drivers 14 and 16, are also connected through output conductors 15 and17 to a summing means 24, and which summing means 24 may be anoperational amplifier such as described with reference to summing means2 for summing the signals from the drivers and for providing a signalcorresponding to the difference therebetween.

Summing means 24 is connected to a delay network 26, and which delaynetwork 26 is connected to a voltage level detector 28. Delay network 26is a low pass filter such as described at pages 42-47, Pulse, Switchingand Digital Waveforms, supra for smoothing and delaying the signal fromsumming means 24 before applying said signal to the level detector.Level detector 28 is an operational amplifier connected as described incopending U.S. application Ser. No. 691,376, filed Dec. 18, 1967 bySteven D. Stolman and assigned to The Bendix Corporation, assignee ofthe present invention, which compares the signal from delay network 26to a preselected reference signal provided by a battery 29, and providesa triggering output when the difference between said signals exceeds apredetermined level. The driver 32, which may be a high input impedanceamplifier such as described with reference to drives 15 and 17, isconnected to level detector 28 and is connected to a brake 34. Brake 34is coupled by suitable mechanical means 36 to the shaft of Motor 8. The

triggering output from level detector 28 is applied through driver 32 tobrake 34, and which brake 34 imparts a holding action to motor 18 forbetter null stability, and during intervals when power to the system iscutoff.

OPERATION As command signal E is received, it is compared by summingmeans 2 with the signal from position sensing device 4 to determine thedifference between the two signals. The difference signal is applied tophase detector which, in accordance with phase of the difference signal,applies a signal to either clockwise driver 14 or counterclockwise 16.The drivers, in turn, actuate switch 23 which delivers full voltage ofappropriate polarity directly to motor 8 for driving said motorclockwise or counterclockwise. Motor 8 receives full voltage as long asan input signal is provided at input 10A of phase detector 10, and assoon as the motor drives through a null, power is cut off. However,inertia carries the motor load past null for providing at the output ofsumming device 2 an opposing signal which reverses the polarity of themotor driving voltage. This first slows down the motor and finallydrivers the motor in the opposite direction until null is againachieved. In contrast to servosystems now shown in the art, the systemof the invention thus provides full voltage to the motor until null isreached and thereby imparts greater accuracy to the system.

At the same time, clockwise and counterclockwise drivers 14 and 16 applysignals to summing device 24 and which device 24 sums the signals andapplies the resulting difference signal to delay network 26 andtherefrom to level detector 28. When the delayed difference signalexceeds a predetermined threshold established by level detector 28,driver 32 actuates brake 34 for better null stability, and also forholding the system at time when power is off.

- Although only one embodiment of the invention has been illustrated anddescribed, various changes in the form and relative arrangements of theparts, which will now appear obvious to those skilled in the art may bemade without departing from the scope of the invention. Reference is,therefore, to be had to the appended claims for a definition of thelimits of the invention.

What I claim is:

1. A servosystem, comprising:

a servomotor;

means connected to the servomotor for providing a motor shaft positionsignal;

means for providing a command signal;

means connected to the shaft position signal means and to the commandsignal means for summing the signals therefrom and providing adifference signal;

a voltage source;

switching means connecting the voltage source to the servomotor;

driving means connected to the switching means;

means for connecting the driving means to the difference signal means,with the driving means responsive to the difference signal above apredetermined level in one sense for rendering the switching meanseffective to apply voltage from the voltage source to the motor;

means for providing an AC reference signal;

the means for connecting the difference signal means to the drivingmeans being connected to the reference signal means for providing afirst signal when the difference signal is of one phase relative to thereference signal and for providing a second signal when said differenceslgnal is of another phase;

the driving means including means responsive to the first signal forproviding a signal for driving the motor in one direction and responsiveto the second signal for providing a signal for driving the motor in anopposite direction;

means connected to the means for providing the motor driving signals forsumming the signals therefrom and for providing a signal correspondingto the difference therebetween; means connected to the difference signalfor filtering said signal;

means for providing a reference signal;

means for comparing the reference signal and the filtered signal toprovide a triggering signal when the difference between the comparedsignals exceeds a predetermined level; and

braking means connected to the triggering signal means and to the motorfor braking the motor in response to the triggering signal.

2. A system as described by claim 1, wherein:

the vgltage source provides voltages of opposite polarities;

the switching means is affected by the signal for driving the motor inthe one direction for applying voltage of one polarity to the motor, andis affected by the signal for driving the motor in theopposite'direction for applying voltage of opposite polarity to themotor.

1. A servosystem, comprising: a servomotor; means connected to theservomotor for pRoviding a motor shaft position signal; means forproviding a command signal; means connected to the shaft position signalmeans and to the command signal means for summing the signals therefromand providing a difference signal; a voltage source; switching meansconnecting the voltage source to the servomotor; driving means connectedto the switching means; means for connecting the driving means to thedifference signal means, with the driving means responsive to thedifference signal above a predetermined level in one sense for renderingthe switching means effective to apply voltage from the voltage sourceto the motor; means for providing an AC reference signal; the means forconnecting the difference signal means to the driving means beingconnected to the reference signal means for providing a first signalwhen the difference signal is of one phase relative to the referencesignal and for providing a second signal when said difference sIgnal isof another phase; the driving means including means responsive to thefirst signal for providing a signal for driving the motor in onedirection and responsive to the second signal for providing a signal fordriving the motor in an opposite direction; means connected to the meansfor providing the motor driving signals for summing the signalstherefrom and for providing a signal corresponding to the differencetherebetween; means connected to the difference signal for filteringsaid signal; means for providing a reference signal; means for comparingthe reference signal and the filtered signal to provide a triggeringsignal when the difference between the compared signals exceeds apredetermined level; and braking means connected to the triggeringsignal means and to the motor for braking the motor in response to thetriggering signal.
 2. A system as described by claim 1, wherein: thevoltage source provides voltages of opposite polarities; and theswitching means is affected by the signal for driving the motor in theone direction for applying voltage of one polarity to the motor, and isaffected by the signal for driving the motor in the opposite directionfor applying voltage of opposite polarity to the motor.